Mark for position detection and mark detecting method and apparatus

ABSTRACT

A mark for position detection formed on a substrate has a first pattern disposed near the center of the mark and having periodicity in a Y-axis direction, and second patterns respectively disposed near both sides of the first pattern in an X-axis direction and each having periodicity in the X-axis direction. The position of the first pattern is detected by aligning the detection center of a detecting optical system, that is, the minimal aberration point of the detecting optical system, with the center of the first pattern. The positions of the second patterns are detected at respective points symmetric with respect to the minimal aberration point, and the detected values for the positions of the second patterns are averaged. An apparatus for detecting the mark for position detection detects the first and second patterns by image processing when the mark is in a stationary state.

This application is a division of prior application Ser. No. 08/966,371filed Nov. 7, 1997 now U.S. Pat. No. 5,966,201.

BACKGROUND OF THE INVENTION

The present invention relates to a mark for position detection and amark detecting method and apparatus, and also relates to an exposuresystem. More particularly, the present invention relates to a mark forposition detection formed on a plane surface of a substrate and a methodand apparatus for detecting the mark, and also relates to an exposuresystem having the mark detecting apparatus as a device for detecting theposition of the substrate. The mark for position detection according tothe present invention is suitable for use in an exposure system to aligna mask pattern and a photosensitive substrate in a photolithographyprocess in which the substrate is exposed in accordance with the maskpattern to produce, for example, a semiconductor device.

In photolithography processes for producing micro devices, e.g.semiconductor devices, liquid-crystal display devices, image pickupdevices (CCDs), or thin-film magnetic heads, a projection exposuresystem is used in which an image of a photomask or a reticle(hereinafter generally referred to as “reticle”), which has a transferpattern formed thereon, is projected onto a substrate coated with aphotosensitive material (photoresist), e.g. a wafer or a glass plate(hereinafter referred to as “wafer”), through a projection opticalsystem.

In this type of projection exposure system, alignment of the reticle andthe wafer must be carried out with high accuracy before exposure. Toperform the alignment, the wafer has marks for position detection(alignment marks) formed (transferred by exposure) in a precedingphotolithography process. By detecting the position of such an alignmentmark, the position of the wafer (or a circuit pattern on the wafer) canbe accurately detected.

The alignment marks on the wafer are entirely unnecessary for theoperating characteristics of the completed micro device. Therefore, itis desirable that the size of the marks be as small as possible.Alignment marks are generally set in the boundary regions between microdevices, which are known as “street lines”, i.e. “margins” for cuttingthe micro devices from each other after the completion of variousprocesses. The street lines are belt-shaped regions each having a widthof the order of from 70 to 90 micrometers. Therefore, the length of eachshorter side of alignment marks is desirably not greater than 70micrometers.

Some methods of detecting the position of a mark on a wafer have alreadybeen put to practical use. The mainstream of recent mark positiondetecting methods is an image detection method in which an optical markimage is detected, and the mark position is detected on the basis of theimage intensity distribution.

Because the above-described alignment requires an extremely high degreeof accuracy, the mainstream of conventional mark position detectingmethods is such that marks (X mark and Y mark) are used exclusively fortwo orthogonal directions (X direction and Y direction), and thepositions of these marks are successively measured. In general,line-and-space patterns having periodicity in the measuring directionshave heretofore been used as the X and Y marks (marks forone-dimensional measurement).

FIGS. 8A and 8B show examples of the conventional marks forone-dimensional measurement. FIG. 8A shows a mark MX used for detectionin the X direction. FIG. 8B shows a mark MY for detection in the Ydirection. These marks MX and MY are used in a pair (there has been nospecific restriction on the positional relationship between the twomarks). In the conventional practice, position detection is firstcarried out with respect to one direction (X direction or Y direction)using one mark, and then position detection is carried out with respectto the other direction (Y direction or X direction) using the othermark.

As has been stated above, the length of each shorter side of these marksis demanded to be not greater than the street line width (in general,from 70 micrometers to 90 micrometers). Therefore, the widths of thesemarks in the non-detecting direction (Y direction for MX; X directionfor MY) have generally been restricted to a length not greater thanabout 70 micrometers from the above restriction.

A mark detecting optical system for detecting the position of a mark asdescribed above needs to be corrected for aberrations to an extremelyhigh degree. The aberration correction includes not only the correctionof aberrations due to errors in designing the optical system but alsothe correction of aberrations due to errors in machining, i.e.decentration of the lens and an error in the surface accuracy. Inparticular, errors in machining are difficult to eliminate completely.Therefore, after the assembly of the optical system, adjustment is madeto minimize the residual aberrations at a specific “mark detectingposition” (one point in the detecting area near the optical axis of thedetecting optical system), thereby reducing the influence of theresidual aberrations during the detection. Accordingly, if the positionfor detecting a mark deviates from the above-described minimalaberration point, a detection error due to the residual aberrationsarises, and the mark detection accuracy degrades.

In the above-described conventional technique, the mark detection forposition detection is carried out with respect to the X and Y directionsseparately from each other. Therefore, it takes a long time to detectthe marks, and this causes the processing capacity (throughput) of theprojection exposure system to be reduced unfavorably.

In view of the above-described circumstances, a conventional techniqueuses two-dimensional marks that enable simultaneous detection withrespect to both the X and Y two-dimensional directions.

FIG. 9 shows one example of two-dimensional marks for detection in boththe X and Y directions. A mark MG shown in FIG. 9 per se has periodicityin two-dimensional directions. However, as will be clear from FIG. 9,the size of the mark edge (boundary between black and white), which iseffective for the position detection in each of the X and Y directions,relative to the mark area undesirably reduces to approximately a half ofthat of one-dimensional marks (MX and MY) because of the periodicity inthe two-dimensional directions. Therefore, the mark area must beincreased in order to obtain a detection accuracy equal to that in thecase of the one-dimensional marks (MX and MY). However, if the mark areais increased, the length of one side (or shorter side) of the markbecomes greater than the street line width (e.g. 100 micrometers or morein the case of FIG. 9), and hence a part of the mark undesirably extendsover the circuit pattern on the wafer. Accordingly, the restriction onthe mark formation position increases unfavorably.

If a two-dimensional mark Mt as shown in FIG. 10 is used in which anX-direction one-dimensional detection mark portion Ma and a Y-directionone-dimensional detection mark portion Mb are disposed in a side-by-siderelation to each other, the length of each shorter side of the mark canbe made not greater than the street line width.

However, the mark Mt shown in FIG. 10 suffers from problems in terms ofthe detection accuracy. That is, the mark detecting optical system hasbeen adjusted such that the residual aberrations are minimized at aspecific “mark detecting position” (one point in the detecting area nearthe optical axis of the detecting optical system), as stated above.Therefore, if a detection mark portion for one direction, e.g. theY-direction detection mark portion Mb (or the X-direction detection markportion Ma), is disposed near the optical axis, the other mark portionMa (or the mark portion Mb) for the other direction lies apart from theoptical axis. Consequently, the detected value for the position of thelatter mark portion Ma (or Mb) is adversely affected by the residualaberrations of the optical system when the position of the mark Mt isdetected with respect to both the X and Y directions simultaneously.Consequently, detection errors increase unfavorably. (This problem willbe described later in more detail to compare the present invention withthe conventional technique in the description of the embodiments).

BRIEF SUMMARY OF THE INVENTION

In view of the above-described circumstances, one object of the presentinvention is to provide a mark for position detection that enables thetime required for mark detection to be shortened and makes it possibleto effect position detection of high accuracy substantiallyindependently of the residual aberrations of a detecting optical system.

Another object of the present invention is to provide an alignment markcapable of meeting a demand for the mark size.

Another object of the present invention is to provide a mark detectingmethod that enables the time required for mark detection to be shortenedand that permits mark position detection to be effected with highaccuracy substantially independently of the residual aberrations of adetecting optical system.

Another object of the present invention is to provide a mark detectingapparatus that enables the time required for mark detection to beshortened and that permits mark position detection to be effected withhigh accuracy substantially independently of the residual aberrations ofa detecting optical system.

Another object of the present invention is to provide an exposure systemcapable of achieving an improvement in the throughput and of realizingregistration of high accuracy.

The present invention provides a mark for position detection arranged asfollows: The mark is formed on a substrate to detect the position of thesubstrate in a predetermined first axis direction (e.g. a Y-axisdirection) and in a second axis direction (e.g. an X-axis direction)perpendicular to the first axis direction. The mark has a first patterndisposed near the center of the mark and having periodicity in the firstaxis direction, and second patterns respectively disposed near bothsides of the first pattern in the second axis direction and each havingperiodicity in the second axis direction.

With the above-described arrangement, the first pattern is detected by adetecting optical system in a state where the detection center of theoptical system is coincident with a predetermined reference point in amark region in which the first pattern is formed (e.g. the center of thefirst pattern). That is, the first pattern is detected at the minimalaberration point of the detecting optical system. At the same time, thesecond patterns are detected at respective points symmetric with respectto the minimal aberration point, and the detected values for thepositions of the second patterns are averaged. Thus, the position in thefirst and second axis directions of the mark for position detection canbe detected with high accuracy substantially independently of theresidual aberrations of the detecting optical system. Accordingly, thetime required for mark detection can be shortened, and moreover,position detection of high accuracy can be effected substantiallyindependently of the residual aberrations of the detecting opticalsystem.

In this case, the period of each of the first and second patterns isdesirably in the range of from about 6 micrometers to about 16micrometers. The reason for this is as follows: The mark for positiondetection is generally formed on the substrate as a step-shaped mark bya photolithography process. Therefore, if the pattern period is smallerthan 6 micrometers, the mark may be undesirably buried by the markforming process. If the pattern period is larger than 16 micrometers,the number of pattern elements of the mark that can be captured on theimage pickup area of an image pickup device (CCD), which is generallyused for the mark detection, becomes excessively small, and thedetection accuracy is degraded. Accordingly, if the pattern period isset in the range of from about 6 micrometers to about 16 micrometers,there are no such problems, and mark position detection of higheraccuracy can be realized.

In these cases, the length of each short side of a mark region in whichthe first and second patterns are formed is desirably in the range offrom about 50 micrometers to about 70 micrometers. The reason for thisis as follows: As stated above, the mark for position detection isgenerally set in a belt-shaped boundary region (street line) betweenmicro devices, which has a width of the order of 70 to 90 micrometers.Considering that a dicing saw used to cut the wafer along the streetline has a width of the order of 70 micrometers at maximum, the lengthof each short side of the mark region is desirably set at a value notgreater than 70 micrometers. By doing so, the mark for positiondetection can readily be formed within the street line. Therefore, themark is not substantially restricted by the mark formation position. Ifthe length of each short side of the mark region is smaller than 50micrometers, the area of the mark becomes excessively small, causing theposition detection accuracy to be degraded.

Therefore, the length of each short side of the mark region ispreferably not less than 50 micrometers. Thus, in a case where thelength of each short side of the mark region is set in the range of fromabout 50 micrometers to 70 micrometers, it is possible to meet a demandfor the mark size satisfactorily.

In addition, the present invention provides a mark detecting method fordetecting the position of the above-described mark for positiondetection in a predetermined first axis direction (e.g. a Y-axisdirection) and in a second axis direction (e.g. an X-axis direction)perpendicular to the first axis direction. The method is characterizedin that the position in the first axis direction of the mark is detectedfrom a mark region near a predetermined detection center, and theposition in the second axis direction of the mark is detected from eachof two mark regions a predetermined distance away from both sides of thedetection center in the second axis direction.

In addition, the present invention provides a mark detecting apparatusfor detecting the position of the above-described mark for positiondetection formed on a substrate in a predetermined first axis direction(e.g. a Y-axis direction) and in a second axis direction (e.g. an X-axisdirection) perpendicular to the first axis direction. The apparatus hasa substrate stage on which the substrate formed with the above-describedmark for position detection is placed, and which is movable in areference plane, together with the substrate placed thereon; an imageprocessing type mark detecting system that photoelectrically detects themark; and an image processor that obtains the position of the mark inthe first and second axis directions by processing a detection signaldetected by the mark detecting system.

By virtue of the above arrangement, the substrate formed with theabove-described mark for position detection is placed on the substratestage; therefore, the mark can be photoelectrically detected by the markdetecting system in a state where the substrate stage is stationary.When the mark is photoelectrically detected by the mark detectingsystem, the image processor processes the detection signal detected bythe mark detecting system, thereby obtaining the position in the firstand second axis directions of the mark. Thus, it is possible to obtainthe position of the mark in the two-dimensional directions in a statewhere the substrate stage is stationary, that is, by a single detectingoperation. To detect the mark by the mark detecting system, thedetection center of the detecting optical system, which constitutes themark detecting system, is made coincident with the center of the firstpattern, which constitutes the mark for position detection. Thus, thefirst pattern is detected at the minimal aberration point of thedetecting optical system. Moreover, the second patterns are detected attwo points symmetric with respect to the minimal aberration point, andthe detected values for the positions of the second patterns areaveraged. Thus, the position of the mark in the first and second axisdirections can be detected with high accuracy substantiallyindependently of the residual aberrations of the detecting opticalsystem.

In addition, the present invention provides an exposure system in whichan image of a pattern formed on a ask is projected by exposure onto asubstrate coated with a photosensitive material through a projectionoptical system. The system has the above-described mark detectingapparatus as a device for detecting the position of the substrate.

The exposure system makes it possible to shorten the time required todetect the position detection mark on the substrate in comparison to theconventional practice that uses one-dimensional marks. Moreover, it ispossible to detect the position of the mark in the first and second axisdirections with high accuracy substantially independently of theresidual aberrations of the detecting optical system, which constitutesthe mark detecting system. Consequently, it becomes possible to achievean improvement in the throughput and an improvement in the alignmentaccuracy and hence possible to improve the overlay accuracy.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic illustration showing the arrangement of aprojection exposure system according to one embodiment of the presentinvention.

FIG. 2 is a detail view showing the arrangement of an alignment sensorin FIG. 1.

FIG. 3 is a schematic illustration showing one example of a mark forposition detection according to the present invention.

FIG. 4 is a schematic illustration for explaining a method of detectingthe mark for position detection in FIG. 3 by the projection exposuresystem according to one embodiment of the present invention.

FIG. 5 is a schematic illustration for explaining a method of detectinga conventional mark for one-dimensional position detection by theprojection exposure system according to one embodiment of the presentinvention.

FIG. 6 is a schematic illustration for explaining the position detectionof a conventional mark for two-dimensional detection.

FIG. 7 is a schematic illustration showing the position detection of amark obtained by rotating the conventional mark for two-dimensionaldetection in FIG. 6 through 90 degrees.

FIGS. 8A and 8B are schematic illustrations showing examples ofconventional marks for one-dimensional measurement, in which

FIG. 8A shows a mark used for detection in an X direction, and

FIG. 8B shows a mark used for detection in a Y direction.

FIG. 9 is a schematic illustration showing one example of conventionaltwo-dimensional marks used for detection in both X and Y directions.

FIG. 10 is a schematic illustration showing another example of theconventional two-dimensional marks.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention will be described below withreference to FIGS. 1 to 7.

FIG. 1 shows a projection exposure system 100 according to oneembodiment of the present invention which has a position detectingapparatus according to the present invention as an off-axis alignmentsensor. The projection exposure system 100 is a step-and-repeat typereduction projection exposure system (so-called stepper).

The projection exposure system 100 has an illumination system IOP; areticle stage RST for holding a reticle R as a mask; a projectionoptical system PL that projects an image of a pattern formed on thereticle R onto a wafer W as a substrate coated with a photosensitivematerial (photoresist); an XY stage 20 as a substrate stage holding thewafer W and moving in a two-dimensional plane (XY-plane), together withthe wafer W; a driving system 22 driving the XY stage 20; and a maincontroller 28 that comprises a minicomputer (or microcomputer) includinga CPU, a ROM, a RAM, an I/O interface, etc. and that overall controlsthe whole system.

The illumination system IOP comprises a light source (a mercury vaporlamp, an excimer laser or the like) and an illumination optical systemincluding a fly's-eye lens, a relay lens, a condenser lens, etc. Theillumination system IOP illuminates the pattern on the lower surface(pattern forming surface) of the reticle R with a uniform illuminancedistribution of illuminating light IL for exposure from the lightsource. As the illuminating light IL for exposure, an emission line,e.g. the i-line from a mercury vapor lamp, or KrF, ArF or other excimerlaser light may be used.

The reticle R is secured to the surface of the reticle stage RST througha securing device (not shown). The reticle stage RST can be finelydriven by a driving system (not shown) in an X-axis direction (adirection perpendicular to the plane of FIG. 1), a Y-axis direction (alateral direction in the plane of FIG. 1) and a 0- direction (adirection of rotation in the XY-plane). Thus, the reticle stage RST,canposition (align) the reticle R such that the center of the pattern ofthe reticle R (reticle center) is approximately coincident with anoptical axis AXp of the projection optical system PL. FIG. 1 shows theprojection exposure system 100 in a state where the reticle alignmenthas been performed.

The projection optical system PL is set such that the optical axis AXpis perpendicular to the plane of travel of the reticle stage RST. Theoptical axis AXp is defined as a Z-axis direction. In this embodiment,the projection optical system PL is telecentric on both sides and has apredetermined reduction magnification β(β is ⅕, for example).Accordingly, if the reticle R is illuminated with a uniform illuminanceby the illuminating light IL in a state where the pattern of the reticleR and a shot area on the wafer W have been aligned, the pattern on thepattern forming surface is projected onto the photoresist-coated surfaceof the wafer W as an image demagnified at the reduction magnification βby the projection optical system PL. In this way, the demagnified imageof the pattern is formed in each shot area on the wafer W.

In actual practice, the XY stage 20 comprises a Y stage that moves inthe Y-axis direction over a base (not shown) and an X stage that movesin the X-axis direction over the Y stage. However, in FIG. 1, the XYstage 20 is shown as a representative of the two stages. A wafer table18 is mounted on the XY stage 20, and the wafer W is held on the wafertable 18 by suction or the like through a wafer holder (not shown).

The wafer table 18 causes the wafer holder holding the wafer W to movefinely in the Z-axis direction. Thus, the wafer table 18 is also knownas “Z stage”. A moving mirror 24 is provided on the upper surface of oneend portion of the wafer table 18. A laser interferometer 26 is providedto face opposite to a reflecting surface of the moving mirror 24. Thelaser interferometer 26 projects a laser beam onto the moving mirror 24and receives the reflected laser beam to thereby measure the position inthe XY-plane of the wafer table 18. It should be noted that in actualpractice there are provided an X moving mirror having a reflectingsurface perpendicularly intersecting the X-axis and a Y moving mirrorhaving a reflecting surface perpendicularly intersecting the Y-axis, andthere are provided an X laser interferometer for position measurement inthe X direction and a Y laser interferometer for position measurement inthe Y direction in association with the X and Y moving mirrors. However,in FIG. 1, the moving mirror 24 is shown as a representative of the Xand Y moving mirrors, and the laser interferometer 26 as arepresentative of the X and Y laser interferometers. Accordingly, it isassumed that in the foregoing description the XY coordinate position ofthe wafer table 18 is measured by the laser interferometer 26.

Measured values obtained from the laser interferometer 26 are suppliedto the main controller 28. The main controller 28 monitors the measuredvalues from the laser interferometer 26, and while doing so, drives theXY stage 20 through the driving system 22, thereby positioning the wafertable 18. In addition, an output of a focus sensor (not shown) is alsosupplied to the main controller 28. The main controller 28 drives thewafer table 18 in the Z-axis direction (focusing direction) through thedriving system 22 on the basis of the output of the focus sensor. Inother words, the wafer W is positioned in the three axis directions,i.e. X, Y and Z, through the wafer table 18.

In addition, a fiducial plate FP is fixed on the wafer table 18 suchthat the surface of the fiducial plate FP is flush with the surface ofthe wafer W. The surface of the fiducial plate FP is formed with variousfiducial marks including those which are used for base line measurementand so forth.

In this embodiment, further, an off-axis alignment sensor AS is providedon a side surface of the projection optical system PL as a markdetecting system that detects a mark for position detection formed onthe wafer W. As the alignment sensor AS, an image processing typeimaging alignment sensor is used.

FIG. 2 shows the arrangement of the alignment sensor AS in detail. Asshown in FIG. 2, the alignment sensor AS includes a detecting opticalsystem 12 that applies illuminating light to a mark MP for positiondetection (described later in detail) formed on the surface of the waferW and also applies illuminating light to index marks formed on an indexboard 52 (described later) used as reference marks to determine thedetection center of the alignment sensor AS. The alignment sensor ASfurther includes a CCD 14 as a two-dimensional image pickup device thatpicks up two-dimensional images of the mark MP and index marks.

The detecting optical system 12 includes a light source 30, a condenserlens 32, a wavelength selecting element 34, an illuminating field stop36, a relay lens 38, an illuminating aperture stop 40, a beam splitter42, an objective lens 44, an imaging aperture stop 46, an imaging lens48, a beam splitter (compound prism) 50, an index board 52, a relay lens54, a light source 56, a condenser lens 58, an index illuminating fieldstop 60, a lens 62, etc. Each constituent part of the detecting opticalsystem 12, together with the operation thereof, will be described below.

The light source 30 is formed by using a halogen lamp or the like thatemits broadband illuminating light. The reason for this is as follows:In the case of an image processing type alignment sensor, ifmonochromatic light is used as a light source, it may be impossible tosurely detect a mark image owing to the effect of thin-film interferenceor the like due to the photoresist coated on the surface of the wafer W.For this reason, a light source that emits incoherent light is used.Accordingly, in a case where there is substantially no effect ofthin-film interference or the like caused by the resist, a laser lightsource that emits laser light may be used as a light source.

Broadband illuminating light emitted from the light source 30 is madeincident on the illuminating field stop 36 through the condenser lens 32and the wavelength selecting element (e.g. a sharp cut filter or aninterference filter) 34.

The wavelength selecting element 34 transmits only a beam of light in awavelength range (e.g. from 550 nanometers to 750 nanometers) to whichthe photoresist coated on the wafer W is not photosensitive (thephotoresist being photosensitive to light of 365 nanometers or 248nanometers, for example). However, in a case where the alignment sensorAS according to this embodiment is used to detect the position of asubstrate not coated with a photoresist, it is unnecessary to preventsuch exposure. Therefore, it is also possible to use a light beam of ashort wavelength close to the wavelength of exposure light. For example,the alignment sensor AS may be used as a device for detecting an overlayerror in registration of a circuit pattern formed on a wafer and aresist pattern formed by transferring a mask pattern image over thecircuit pattern by exposure light and developing the transferred maskpattern image.

Illuminating light DL passing through a transmitting part of theilluminating field stop 36 enters the illuminating aperture stop 40through the relay lens 38. Then, the illuminating light DL is reflectedvertically downward by the beam splitter 42 to pass the objective lens44 disposed on the wafer side of the beam splitter 42. Thereafter, theilluminating light DL illuminates an illumination area containing themark MP for position detection formed on the wafer W.

The mark MP for position detection is a planar mark as shown in FIG. 3(described later). However, in many cases, such a mark for positiondetection is formed on the wafer W as not a planar mark but astep-shaped mark in which a mark portion and the other portion define astep.

The illuminating field stop 36 is practically in a conjugate relation(image-formation relation) to the surface (mark MP for positiondetection) of the wafer W. Therefore, the illumination area on the waferW can be limited according to the shape and size of the transmittingpart of the illuminating field stop 36.

A light beam reflected from the illumination area on the wafer W, whichcontains the mark MP for position detection, passes successively throughthe objective lens 44 and the beam splitter 42 to reach the imagingaperture stop 46. After passing through the imaging aperture stop 46,the light beam is converged by the imaging lens 48 and passes throughthe beam splitter 50 to form an image of the mark MP for positiondetection on the index board 52.

The index board 52 has a total of four index marks provided atpredetermined positions, respectively. The index marks include indexmarks 52 a and 52 b serving as reference marks for mark positiondetection in the X direction and index marks 52 c and 52 d serving asreference marks for mark position detection in the Y direction. The fourindex marks 52 a, 52 b, 52 c and 52 d are positioned so as to surroundan optical axis AXa of the detecting optical system 12 (however, in FIG.2 only the X-direction index marks 52 a and 52 b are shown; for all thefour index marks 52 a, 52 b, 52 c and 52 d, see FIG. 4). Thus, thealignment sensor AS is adapted to detect the position of the mark MP inboth the X and Y directions simultaneously.

The index marks 52 a, 52 b, 52 c and 52 d are illuminated by an indexboard illuminating system 13 described below. The index boardilluminating system 13 includes a light source 56, e.g. a light-emittingdiode (LED), a condenser lens 58, an index illuminating field stop 60, alens 62, etc. The shape of a transmitting part of the index illuminatingfield stop 60 is so selected that, after being reflected by the beamsplitter 50, illuminating light from the index board illuminating system13 illuminates only a small area containing the index marks 52 a, 52 b,52 c and 52 d.

In contrast, the shape of the transmitting part of the illuminatingfield stop 36 is so selected that illuminating light does not illuminatethe small area containing the index marks 52 a, 52 b, 52 c and 52 d(i.e. so as to shield the small area from the illuminating light).Therefore, a two-dimensional image of the mark MP for position detectionand a two-dimensional image of the index marks 52 a, 52 b, 52 c and 52 dcan be formed separately from each other. Consequently, thetwo-dimensional images of the two different kinds of mark are notduplicated by different illumination systems. Thus, it becomes possibleto detect the positions of the marks surely and highly accurately.

Light from the image of the position detection mark MP formed on theindex board 52 and light from the index marks 52 a, 52 b, 52 c and 52 don the index board 52 are focused onto the CCD 14 through the relay lens54 to form respective two-dimensional images on the image pickup surfaceof the CCD 14.

An image signal DS from the alignment sensor AS (more specifically, fromthe CCD 14), which is formed as described above, is supplied to an imageprocessor 16 in the subsequent stage. The image processor 16 detects theposition of the mark MP for position detection on the wafer W (i.e. therelative position of the mark MP with respect to the index center) onthe basis of the image signal from the CCD 14, that is, on the basis ofthe distance between the image of the position detection mark MP and theimage of the index marks 52 a and 52 b (or the distance between theimage of the position detection mark MP and the image of the index marks52 c and 52d). Then, the image processor 16 transmits the detectedposition of the position detection mark MP to a main controller 28.

Next, one example of marks for position detection according to thepresent invention formed on the wafer W will be described with referenceto FIG. 3. A mark MP shown in FIG. 3 comprises a first mark portion M1as a first pattern which is disposed in the center in the X-axisdirection (second axis direction) of a mark forming region and which hasperiodicity in the Y-axis direction (first axis direction), and a pairof second mark portions M2 a and M2 b as second patterns which arerespectively disposed on both sides of the first mark portion M1 in theX-axis direction perpendicular to the Y-axis direction and which haveperiodicity in the X-axis direction. The first mark portion M1 is usedfor position measurement in the Y-axis direction, and the second markportions M2 a and M2 b are used for position detection in the X-axisdirection. The pitch of mark elements constituting each of the markportions M1, M2 a and M2 b is, for example, of the order of 12micrometers (6 micrometer line and space).

It should be noted that the pitch of the mark elements of the markportions M1, M2 a and M2 b is not necessarily limited to 12 micrometers,but a finer pitch may be used. However, an excessively fine pitch maycause the mark elements to be undesirably indistinguishable byplanarization carried out in the micro device manufacturing process,resulting in the mark portions M1, M2 a and M2 b being lost. For thisreason, it is desirable that the pitch of the mark elements of the markportions M1, M2 a and M2 b be not smaller than 6 micrometers.

The pitch of the mark elements of the mark portions M1, M2 a and M2 bmay be set at a larger value. However, as the pitch becomes larger, thenumber of mark elements of the mark portions M1, M2 a and M2 b that canbe disposed in the street line area decreases, and it becomes difficultto obtain the averaging effect. Therefore, it is desirable that thepitch of the mark elements of the mark portions M1, M2 a and M2 b be notlarger than about 16 micrometers.

As has been stated above, the length of each short side of marks forposition detection is demanded to be not larger than the street linewidth (in general, from 70 to 90 micrometers). As shown in FIG. 3, themark MP for position detection according to the present invention canreduce the mark width in either of the X- and Y-axis directions (in FIG.3, the mark width in the Y-axis direction) to a value not larger thanabout 70 micrometers. The length in the other direction becomes slightlylarger than that of the conventional one-dimensional marks. However,this causes no problem because there is no restriction in the lengthwisedirection with regard to the street line.

A method of detecting the mark MP for position detection by theprojection exposure system 100 according to this embodiment will bedescribed below with reference to FIG. 4.

In this embodiment, the index board 52 is provided with a total of fourindex marks as shown in FIG. 4, i.e. index marks 52 a and 52 b for the Xdirection and index marks 52 c and 52 d for the Y direction, which aredisposed at respective positions such that the index marks 52 a and 52 bface each other across the optical axis AXa of the detecting opticalsystem 12, and the index marks 52 c and 52 d face each other across theoptical axis AXa.

To perform position detection, the wafer W is set by rough alignmentsuch that the center of the mark MP for position detection isapproximately coincident with the optical axis AXa of the detectingoptical system 12. The rough alignment enables the wafer W to be alignedwith an accuracy of the order of ±1 micrometer at worst according to theaccuracy of a typical search alignment mechanism in the present state ofart, although the rough alignment accuracy depends on the accuracy of asearch alignment mechanism (not shown).

As a result of the rough alignment, an image of the position detectionmark MP and an image of the index marks 52 a, 52 b, 52 c and 52 d, whichare provided on the index board 52, are formed on the image pickupdevice 14 with a positional relationship as shown in FIG. 4. The imageprocessor 16 executes image processing on images of specific regions ofthese images, i.e. an image of an X-direction detecting area DXsurrounded by a broken line rectangle and an image of a Y-directiondetecting area DY similarly surrounded by a broken line rectangle. Theimage processor 16 detects a positional relationship between the indexmarks 52 a and 52 b and the mark portions M2 a and M2 b from the imageof the detecting area DX and a positional relationship (relativeposition) between the index marks 52 c and 52 d and the mark portion M1from the image of the detecting area DY. The relative position betweenthe index marks 52 a and 52 b and the mark portions M2 a and M2 b is adetected value in the X direction of the mark MP for position detection,and the positional relationship (relative position) between the indexmarks 52 c and 52 d and the mark portion M1 is a detected value in the Ydirection of the mark MP.

To detect the position of each of the index marks 52 a, 52 b, 52 c and52 d and mark portions M1, M2 a and M2 b , a conventional detectionalgorithm, e.g. the slice method or the correlative method, should beused. The image of the X-direction detecting area DX contains the imageof the Y-direction mark portion M1, which is unrelated to the detectionin the X direction. In this regard, the detection algorithm in the imageprocessor 16 should be set such that during the position detection inthe X direction, only the images of the index marks 52 a and 52 b andsecond mark portions M2 a and M2 b are processed. More specifically, inthe image of the X-direction detecting area DX, the contrast change inthe first mark portion M1 is smaller than the contrast change in theX-direction mark portions M2 a and M2 b (i.e. the contrast change isabout a half of the latter). Accordingly, the level of the signalintensity in the mark portion M1 is lower than that of the signalintensity in the mark portions M2 a and M2 b . Therefore, it isconceivable to set the slice level higher than the level of the signalintensity in the mark portion M1, by way of example.

The distance between the index marks 52 a and 52 b on the index board 52is set sufficiently long to put the mark MP therebetween. The distancebetween the index marks 52 c and 52 d may be set to put only the markportion M1 therebetween. In actual practice, however, the mark MP may benecessary to be formed not in a street line extending in the X directionbut in a street line extending in the Y direction, depending upon thedesign of semiconductor devices to be formed on the wafer W. In such acase, a mark obtained by rotating the mark MP in FIG. 3 through 90degrees is used. Therefore, it is desirable that the distance betweenthe index marks 52 c and 52 d be also sufficiently long to put the 90degree-rotated mark MP therebetween.

The detecting optical system 12 constituting the alignment sensor ASaccording to this embodiment is adjusted during assembly such that theresidual aberrations are minimized at the position of the optical axisAXa. Accordingly, the Y-direction detection mark portion M1 in FIG. 4 isdetected at a point where the residual aberrations are minimal.Therefore, the detection of the Y-direction detection mark portion M1 ispractically independent of a position detection error due to theresidual aberrations. On the other hand, detection of the X-directiondetection mark portions M2 a and M2 b is carried out at a position awayfrom the optical axis AXa. Accordingly, detection of these marksinvolves an error due to the residual aberrations. However, the two markportions M2 a and M2 b are disposed symmetrically with respect to theoptical axis AXa, and hence the adverse effects of the residualaberrations on the detection of the two mark portions M2 a and M2 b areapproximately symmetric. Therefore, the influence of the residualaberrations can be substantially canceled by averaging the detectedvalues for the positions of the two mark portions M2 a and M2 b . Thus,it is possible according to this embodiment to realize a positiondetecting system having almost no detection error due to the residualaberrations. The same is true in the case of using a mark obtained byrotating the mark MP shown in FIG. 3 through 90 degrees.

Next, a method of detecting the position of a conventional mark forone-dimensional position detection by the same projection exposuresystem 100 as that used in this embodiment will be described withreference to FIG. 5. In the figure, index marks 25 a, 25 b, 25 c and 25d correspond to the index marks 52 a, 52 b, 52 c and 52 d, respectively.

In this case also, the wafer W is roughly aligned so that the center ofa conventional mark MX for one-dimensional position detection in the Xdirection is approximately coincident with the optical axis AXa of thedetecting optical system 12. Then, the position in the X-direction ofthe mark MX for position detection is detected on the basis of the imageof the X-direction detecting area DX. Regarding the detection of a markMY (FIG. 8A) for position detection in the Y direction also, theposition of the mark MY is similarly detected on the basis of the imageof the Y-direction detecting area DY. In the case of detecting thesemarks also, position detection of high accuracy can be effected withoutsubstantially being influenced by the residual aberrations because thedetection can be carried out in areas near the optical axis AXa.Accordingly, it is possible to detect the position of the conventionalone-dimensional mark without changing the detecting optical system 12,which is adapted to detect the mark MP for two-dimensional detection.

To compare the mark MP with a conventional mark for position detectionshown in FIG. 10, position detection of the conventional mark Mt fortwo-dimensional detection will be described below with reference to FIG.6. To detect the mark Mt in both the X and Y directions simultaneously,four index marks (index marks 53 a, 53 b, 53 c and 53 d) are disposed onan index board 53 (not shown; corresponding to the index board 52) asshown in FIG. 6. In detection of the mark Mt, however, if the markportion Mb for detection in the Y direction is disposed near the opticalaxis AXa, the mark portion Ma for detection in the X direction ispositioned away from the optical axis AXa. Consequently, the detectedvalue for the position of the mark portion Ma is adversely affected bythe residual aberrations of the optical system.

In a case where a mark Mr obtained by rotating the mark Mt in FIG. 10through 90 degrees is used in accordance with the orientation of astreet line, as shown in FIG. 7, if the mark portion Mc for detection inthe X direction is disposed near the optical axis AXa, the mark portionMd for detection in the Y direction is positioned away from the opticalaxis AXa. Accordingly, the detected value for the position of the markportion Md is adversely affected by the residual aberrations as in thecase of the mark portion Ma. It should be noted that index marks 28 athrough 28 d in FIG. 7 correspond to the index marks 52 a through 52 d,respectively.

In contrast, the mark MP according to the present invention enablessimultaneous detection in both the X and Y directions with high accuracywithout being adversely affected substantially by the residualaberrations of the detecting optical system 12, as stated above.

Although, in the foregoing description, where the residual aberrationsof the detecting optical system 12 are minimized is the position of theoptical axis of the detecting optical system 12, it should be noted thatin a case where the mark detection center position (i.e. the center ofthe surrounding index marks 52 a, 52 b, 52 c and 52 d) deviates from theoptical axis AXa, it is desirable to adjust the detecting optical system12 such that the residual aberrations are minimized at the markdetection center position.

Next, the flow of the operation during exposure of the projectionexposure system arranged as described above will be briefly described.

After the wafer W has been loaded on the wafer table 18 by a waferloader (not shown), rough positioning (search alignment) of the wafer Wis performed by the search alignment mechanism (not shown). Morespecifically, the search alignment is effected, for example, on thebasis of the outer shape of the wafer W, or by detecting searchalignment marks on the wafer W. In this embodiment also, the searchalignment is carried out in the same way as in the conventionalpractice; therefore, a detailed description thereof is omitted.

Prior to overlay exposure, base line measurement is carried out tomeasure a positional relationship between the detection center (i.e. thecenter of the surrounding index marks as stated above) of the alignmentsensor AS that detects a mark for position detection on the wafer W andthe center of the projection optical system PL (in general, the centerof the projection optical system PL is coincident with the reticlecenter as the center of the reticle pattern). More specifically, thebase line measurement is carried out as follows:

1 The fiducial plate FP provided on the wafer table 18 is moved to aposition where an image of a reticle alignment mark (not shown) isprojected through the projection optical system PL. The movement of thefiducial plate FP is effected by moving the XY stage 20 through thedriving system 22 under the control of the main controller 28. As statedabove, the surface of the fiducial plate FP is approximately flush withthe surface of the wafer W (in the optical axis direction), and thefiducial plate FP has fiducial marks (not shown) formed on the surfacethereof. At this time, a relative position between the reticle alignmentmark and a fiducial mark on the fiducial plate FP is detected, forexample, by a reticle microscope (not shown) through the projectionoptical system PL.

The position of the wafer table 18 at this time is measured by the laserinterferometer 26 through the moving mirror 24 provided on the wafertable 18, and the result of the measurement is sent to the maincontroller 28. The main controller 28 adds the result of the measurementby the laser interferometer 26 and the relative position outputted fromthe reticle microscope and stores the resulting sum as the reticleposition in the RAM.

2 Next, the main controller 28 drives the wafer table 18 together withthe XY stage 20 as one unit through the driving system 22 to move thefiducial plate FP to a position near the detection reference position ofthe alignment sensor AS. Then, the system detects a positionalrelationship between the center (detection center) of the index marks onthe index board 52 incorporated in the alignment sensor AS and afiducial mark on the fiducial plate FP. The detected value for thepositional relationship and the output value of the laser interferometer26 (i.e. the position of the wafer table 18) at this time are sent tothe main controller 28. The main controller 28 adds the detected valueand the output value and defines the resulting sum as the alignmentsensor position. Moreover, the main controller 28 determines adifference between the reticle position and the alignment sensorposition and stores the difference as “measured base line value” in theRAM.

After the above sequence of base line measurement, overlay exposure ontothe waver W is initiated. That is, the position of the mark MP forposition detection on the wafer W is detected by the alignment sensor ASas described above. In this embodiment, the position of the mark MP canbe detected in both the X and Y directions simultaneously. Accordingly,the position measurement can be carried out in a short period of time incomparison to the conventional practice.

The main controller 28 adds the positional relationship between the markMP for position detection and the center of the index marks in thealignment sensor AS and the position of the wafer table 18 (i.e. theoutput value from the laser interferometer 26) at this time andrecognizes the resulting sum as the mark position.

Subsequently, the main controller 28 moves the wafer W (i.e. the wafertable 18) from this position by a distance corresponding to the sum ofthe base line quantity and the designed coordinate values of theposition detection mark MP, relying on the measured value from the laserinterferometer 26.

Thus, the projected image of the pattern on the reticle R and theexisting pattern on the wafer W are accurately aligned with each other.In this state, exposure is carried out to project and thereby transferthe pattern on the reticle R onto the wafer W.

In this way, each shot area on the wafer W is successively moved to theposition where the image of the reticle pattern is projected, andexposure (projection transfer) is repeated. Thus, step-and-repeatexposure is performed.

As has been described above, the mark MP for position detectionaccording to the present invention makes it possible to detect theposition of the mark MP in both the X and Y directions simultaneouslyand also enables the length of each short side of the mark MP to bereduced to a value not greater than the width of an ordinary streetline. Therefore, a mark for simultaneous position detection in twodirections can be disposed without a need of providing a new area for amark for position detection on the wafer W. Moreover, because the timerequired for mark position detection can be shortened, it becomespossible to improve the throughput of the projection exposure system100.

In addition, the mark MP has mark portions for detection in the X- andY-axis directions, respectively. For one of the two directions, theposition of a mark portion of the mark P is detected at the minimalaberration point of the alignment sensor AS. For the other direction,the positions of two mark portions of the mark MP are detected atrespective points symmetric with respect to the minimal aberrationpoint, and the detected values for the positions of the two markportions are averaged. Therefore, highly accurate position detection canbe effected without being adversely affected substantially by theresidual aberrations of the detecting optical system. Accordingly, it ispossible to improve the accuracy of alignment (registration) of aprojected image of the pattern on the reticle R and an existing patternon the wafer W during the exposure, which is performed by using theresult of the position detection of the mark MP.

Although in the foregoing embodiment the position detection of the markMP is carried out by using the index marks 52 a, 52 b, 52 c and 52 dformed on the index board 52 as position references, it should be notedthat the positions of the pixels of the image pickup device 14 (e.g. theimage pickup pixels of a CCD) may be used as references for detectionwithout using index marks such as those described above. In such a case,it is possible to omit the index illuminating system 56 through 62 inthe detecting optical system 12 shown in FIG. 2.

The above-described step-and-repeat exposure operation may be carriedout by an EGA (Enhanced Global Alignment) method in which, prior toexposure, marks for position detection in a plurality of shot areas aredetected, and the detected values are statistically processed todetermine an array of exposure shot areas, and then exposure is carriedout for all shot areas on the basis of the exposure shot array.Alternatively, the exposure operation may be carried out by a die-by-diemethod in which a mark for position detection provided in each shot areaon a wafer W is detected for each shot area to carry out overlayexposure for the shot area.

Although in the foregoing embodiment the mark for position detection andmark detecting apparatus according to the present invention are appliedto a step-and-repeat projection exposure system, the mark for positiondetection and mark detecting apparatus according to the presentinvention are not necessarily limited thereto, but may also suitably beapplied to step-and-scan projection exposure systems and other exposuresystems.

As partially touched on before, in exposure apparatuses to which thepresent invention can be applied, which are of the step and repeat type,step and scan type, the mirror projection type and the like,illumination light for exposure can be selected from bright lines (e.g.,g and i lines) of a mercury lamp, excimer laser (e.g., KrF excimer laserof 248 nm, ArF excimer laser of 193 nm and F₂ excimer laser of 157 nm),and higher harmonics of YAG laser (or metal vapor laser) and the like.EUV (Extreme Ultra Violet) light of the wavelength range of 5-15nanometers may also be used. The present invention can also be appliedto X-ray exposure apparatuses and electronic ray exposure apparatuses.

Furthermore, in a photolithography process for producing microdevices,such as semiconductor devices, images of patterns formed on ten-oddreticles, respectively, are successively transferred onto asemiconductor wafer in a overlaying manner. The images of the patternsare formed on a plurality of layers laid on the wafer, respectively.More specifically, an image of a first pattern of a first reticle isformed on a first layer on the wafer and then an image of a secondpattern of a second reticle is formed on a second layer which has beenlaid on the first layer so that the images of the first and secondpatterns are in a predetermined alignment. In order to carry out anaccurate alignment between the transferred first and second patterns, analignment mark which has been formed on the first layer when the firstpattern image is formed is detected to determine its position and thenthe second reticle and the wafer are moved relative to each other basedon the thus determined position of the alignment mark. By thisoperation, the second pattern is transferred onto the second layer whichis a photoresist layer on the first layer while the transferred secondpatterns being aligned with the transferred first pattern. Asappreciated from the foregoing, the first reticle has an alignment markas well as the first pattern for carrying out alignment between thesemiconductor wafer and the second reticle and hence between thetransferred first pattern on the first layer and the second pattern. Itwill be understood from the foregoing that an alignment mark of thepresent invention (FIG. 3) is formed not only on a substrate such assemiconductor wafer and glass plate on which microdevices (such assemiconductor devices, liquid-crystal display devices, image pickupdevices (CCDs) and thin-film magnetic heads) are formed, but also on areticle on which a device pattern is depicted. In short, an alignmentmark according to this invention can be applied to both of a substratecoated with photoresist and a reticle (mask) having a device pattern tobe transferred to the substrate.

As has been described above, the present invention makes it possible toprovide a novel, excellent mark for position detection that allows thetime required for mark detection to be shortened and enables highlyaccurate position detection substantially independent of the residualaberrations of a detecting optical system.

What is claimed is:
 1. An exposure method comprising the steps of:preparing an orthogonal coordinate system including first and secondaxes perpendicular to each other; placing an object with a mark in saidorthogonal coordinate system, said mark including a first patterncomprising a plurality of bar-like patterns spaced from each other atpredetermined intervals in said first axis direction and extending withlonger continuity in said second axis direction than in said first axisdirection, and second patterns disposed near both sides of said firstpattern in said second axis direction and comprising a plurality ofbar-like patterns spaced from each other at predetermined intervals insaid second axis direction and extending with longer continuity in saidfirst axis direction than in said second axis direction; directing adetection beam to said mark; detecting the detection beam reflected fromsaid mark through a detecting optical system, said first pattern of saidmark being detected though a portion where aberrations of the detectingoptical system are minimized; attaining information with respect to theposition of said object based on said detection beam; and determiningthe position of said object with respect to said first and second axesbased on said information.
 2. An exposure method according to claim 1,said attaining step comprising: detecting photoelectrically said mark;and processing a signal detected in said detecting step to therebyattain information with respect to a position of said mark in said firstand second axis directions.
 3. An exposure method according to claim 2,said attaining step comprising: detecting photoelectrically said firstpattern and second patterns in parallel.
 4. An exposure method accordingto claim 2, wherein said attaining step comprises; achieving an imagepickup process for said mark; and attaining information with respect tothe position of said mark in said first and second axis direction basedon the result of said image pickup process.
 5. An exposure methodaccording to claim 4, wherein said portion where the aberrations areminimized includes an optical axis of said detecting optical device. 6.An exposure method according to claim 4, said attaining step comprising:obtaining a position of said mark in said second axis direction byaveraging data obtained from said second patterns.
 7. An exposure methodaccording to claim 4, said attaining step comprising: attaining saidinformation when a stage on which said object is placed is in astationary state.
 8. An exposure method according to claim 4, saidattaining step comprising: processing only a detection signal obtainedfrom said second pattern in obtaining a position of said mark in saidsecond axis direction.
 9. An exposure method according to claim 8, saidattaining step comprising: setting up a slice level of said detectionsignal, with which a position of said mark is obtained in said secondaxis direction, higher than a predetermined value.
 10. An exposuremethod according to claim 9, wherein said predetermined value is thelevel of a detection signal above which said first pattern is detectedin detecting said second axis direction.
 11. An exposure methodaccording to claim 1, further comprising: projecting a predeterminedpattern onto said object through a projection optical system; whereinsaid attaining step comprises detecting said mark with an objectiveoptical system which is independent from said projection optical system.12. An exposure method according to claim 1, wherein said first patternis disposed near a center in said second axis direction of said mark.13. An exposure method according to claim 1, wherein said first patternis disposed near a center of said mark for position detection.
 14. Anexposure method according to claim 1, wherein said second patterns aredisposed in a symmetric relation to each other with respect to a centerin said second axis direction of said mark.
 15. An exposure methodaccording to claim 13, wherein said second patterns are disposed in asymmetric relation to each other with respect to a center of said mark.16. An exposure method according to claim 1, wherein said first patternis utilized to detect a position in said first axis direction of saidobject, and said second patterns are utilized to detect a position insaid second axis direction of said object.
 17. An exposure methodaccording to claim 1, wherein said first pattern has periodicity only insaid first axis direction, and said second patterns have periodicityonly in said second axis direction.
 18. An exposure method according toclaim 1, wherein said object comprises a substrate.
 19. A method formanufacturing a device including a step of exposing predeterminedpattern onto a substrate by using the exposure method of claim
 1. 20. Amethod for manufacturing an exposure apparatus comprising the steps of:providing a mark detecting device which detects a position of a markformed on an object with relation to first and second axes perpendicularto each other, said mark has a first pattern comprising a plurality ofbar-like patterns spaced from each other at predetermined intervals insaid first axis direction and extending with longer continuity in saidsecond axis direction than in said first axis direction, and secondpatterns disposed near both sides of said first pattern in said secondaxis direction and comprising a plurality of bar-like patterns spacedfrom each other at predetermined intervals in said second axis directionand extending with longer continuity in said first axis direction thanin said second axis direction, said mark detecting device including adetecting optical system, said mark detecting device detecting saidfirst pattern through a portion where aberrations of the detectingoptical are minimized; and providing a position detecting apparatusconnected electrically with said mark detecting device so that theposition detecting apparatus determines, a position of said object onthe basis of a detection signal detected by said mark detecting device.21. A method for manufacturing an exposure apparatus according to claim20, further comprising: providing a projection optical system whichprojects a predetermined pattern onto said object, wherein said markdetecting device has an objective optical system which is independentfrom said projection optical system.
 22. A method for manufacturing anexposure apparatus to claim 21, wherein said mark detecting deviceachieves an image pickup process for said mark.
 23. A method formanufacturing an exposure apparatus according to claim 20, wherein saidobject comprises a substrate, and said mark detecting device includes alight source which generates light of wide band having a component ofwavelengths different from those to which said substrate is sensitive.24. A method for manufacturing an exposure apparatus according to claim20, wherein said portion where the aberrations are minimized includes anoptical axis of said detecting optical system.
 25. An exposure methodcomprising the steps of: preparing a mark detecting device having adetecting optical system; disposing a central mark region of a markformed on an object, for being detected its position with relation tofirst and second axes perpendicular to each other, near a portion whereaberrations of said detecting optical system are minimized; directing adetection beam to said mark; detecting a position in said first axisdirection of said mark by using said detection beam reflected from saidcentral mark region, and detecting a position in said second axisdirection of said mark by using said detection beam reflected from markregions which are placed adjacent to both sides of said central markregion in said second axis direction.
 26. An exposure method accordingto claim 25, wherein said central mark region is aligned with an opticalaxis of said detecting optical system, and said mark regions adjacent tosaid central mark region are positioned symmetrically with respect tosaid optical axis.
 27. An exposure method according to claim 25, whereinsaid mark detecting step comprising: detecting photoelectrically saidmark to thereby receive a detection signal; and obtaining a position ofsaid mark with respect to said first and second axis directions byprocessing said detection signal.
 28. An exposure method according toclaim 27, wherein said detecting step comprises: achieving an imagepickup process for said mark; and attaining information with respect tothe position of said mark in said first and second axis directions basedon the result of said image pickup process.
 29. An exposure methodaccording to claim 25, further comprising: projecting a predeterminedpattern onto said object through a projection optical system; andwherein said mark detecting step comprises the step of detecting saidmark through an objective optical system which is independent from saidprojection optical system.
 30. An exposure method according to claim 25,wherein said object comprises a substrate, and said detection beamcomprises light of wide band having a component of wavelengths differentfrom those to which said substrate is sensitive.
 31. An exposure methodaccording to claim 25, wherein in said central mark region, there isprovided with a first pattern comprising a plurality of bar-likepatterns spaced from each other at predetermined intervals in said firstaxis direction and extending with longer continuity in said second axisdirection than in said first axis direction; and in both sides of saidcentral mark region, there are provided with second patterns comprisinga plurality of bar-like patterns spaced from each other at predeterminedintervals in said second axis direction and extending with longercontinuity in said first axis; direction than in said second axisdirection.
 32. An exposure method according to claim 25, wherein saidfirst pattern has periodicity only in said first axis direction, andsaid second patterns have periodicity only in said second axisdirection.
 33. A method for manufacturing a device including a step ofexposing a predetermined pattern onto a substrate by using the exposuremethod of claim
 25. 34. A method for manufacturing an exposure apparatuscomprising: providing a mark detecting device which detects a positionof a mark formed on an object with relation to first and second axesperpendicular to each other, said mark detecting device having adetection optical system, wherein said mark detecting device detects aposition in said first axis direction of said mark while disposing acentral mark region of said mark near a portion where aberrations of thedetecting optical system are minimized, and detects a position in saidsecond axis direction of said mark by observing mark regions which areplaced adjacent to both sides of said central mark region in said secondaxis direction; and providing a position detecting apparatus connectedelectrically with said mark detecting device so that the positiondetecting apparatus determines, a position of said object on the basisof a detection signal detected by said mark detecting device.
 35. Amethod for manufacturing an exposure apparatus according to claim 34,further comprising: providing a projection optical system for projectinga predetermined pattern onto said object, wherein said mark detectingdevice has an objective optical system which is independent from saidprojection optical system.
 36. A method for manufacturing an exposureapparatus according to claim 34, wherein said object comprises asubstrate, and said mark detecting device generates light of wide bandhaving a component of wavelengths different from those to which saidsubstrate is sensitive.
 37. A method for manufacturing an exposureapparatus according to claim 34, wherein said mark detecting achieves animage pickup process for said mark.
 38. A method for manufacturing anexposure apparatus according to claim 34, wherein said portion where theaberrations are minimized includes an optical axis of said detectingoptical system.